1. Field of the Invention
The present invention relates generally to a multimedia broadcast/multicast service (MBMS) for a mobile communication system, and more particularly to a paging method for indicating the presence of control information on an MBMS.
2. Description of the Related Art
Currently, a code division multiple access (CDMA) mobile communication system provides a voice service and a packet service for transmitting mass storage data. Further, the CDMA mobile communication system has been developed into a multimedia broadcast/communication system capable of providing multimedia services. Additionally, a broadcast service has been suggested for providing services from at least one multimedia data source to a plurality of user equipments (UEs). The broadcast service includes a multimedia broadcast/multicast service (MBMS) proposed by the 3rd generation project partnership (3GPP).
The MBMS uses a multimedia transmission mode for transmitting data, such as real time images, voice data, still images, and characters. Thus, the MBMS may require sufficient transmission resources. Because a plurality of UEs may request the same MBMS, the MBMS is provided through a broadcasting channel.
The MBMS can be provided through two types of services, i.e., a point to point (PtP) service or a point to multi-point (PtM) service. In the PtP service, a dedicated channel must be assigned to each UE, and in the PtM service, a common channel must be assigned to UEs requesting the same MBMS.
FIG. 1 illustrates conventional UTRAN for providing the MBMS. Referring to FIG. 1, a UE 130 directly receives the MBMS and has hardware or software for supporting the MBMS. The UTRAN is a radio communication network for connecting the UE 130 to a CN 100. The UTRAN includes a plurality of radio network systems (RNSs) 110 and 120. The RNS 110 includes an RNC 111 and a plurality of nodes B 113 and 115 controlled by the RNC 111 and the RNS 120 includes an RNC 112 and a plurality of nodes B 114 and 116 controlled by the RNC 112. That is, the RNS 110 includes the RNC 111, a first node B 113, and a second node B 115 controlled by the RNC 111, and a plurality of cells controlled by the first node B 113 and the second node B 115. Similarly, the RNS 120 includes the RNC 112, a third node B 114 and a fourth node B 116 controlled by the RNC 112, and a plurality of cells controlled by the third node B 114 and the fourth node B 116. Typically, the total number of node Bs controlled by an RNC, and the total number of cells included in node Bs are determined according to a service provider, and performance of the RNC and the nodes B.
The UE 130 is connected to the UTRAN through a Uu interface 121 and the UTRAN is connected to the CN 100 through an Iu interface 122. Table 1 shows interfaces for connecting nodes to each other. The names for the interfaces shown in table 1 are stipulated in the 3GPP standard and may change.
TABLE 1Interface NameFunctionUuInterface between UE and UTRANIuInterface between UTRAN and CNGrInterface between SGSN and HLRGn/GpInterface between SGSN and GGSNGiInterface between GGSN and BM-SCGn/GpInterface between BM-SC and CP
FIG. 2 schematically illustrates a structure of a UTRAN protocol. Referring to FIG. 2, messages of the upper layer processed in the UTRAN can be broadly classified as control data or user data.
In FIG. 2, the messages of the upper layer of the UTRAN are represented as a control plain (C-Plain) signaling 201 and user plain (U-Plain) data 202. The C-plain signaling 201 and the U-plain data 202 are messages of a non-access stratum (NAS). The NAS messages are not used for a radio connection between the UE and the UTRAN and the UTRAN does not necessary to know the contents of the NAS messages. Alternatively, messages used for the radio connection between the UE and the UTRAN are called access stratum (AS) messages, which are data or control signals used at an area below a radio resource control (RRC) 203.
The RRC 203 controls a physical layer (L1) relating to a connection between the UE and the UTRAN, a medium access control of layer 2 (L2/MAC), a radio link control of layer 2 (L2/RLC), a packet data convergency protocol of layer 2 (L2/PDCP), and a broadcast/multicast control of layer 2 (L2/BMC). Further, the RRC 203 controls the connection between the UE and the UTRAN, such as a physical call setting, a logical call setting, control information transmission/reception, and specific data transmission/reception between the UE and the UTRAN.
The L2/PDCP 204 receives data from an NAS layer and transmits the data to the L2/RLC 206 using a predetermined protocol. The L2/BMC 205 receives data required for the broadcast and multi-broadcast from the NAS layer and transmits the data to the L2/RLC 206 by using a predetermined protocol. The L2/RLC 206 receives a control message, which is transmitted to the UE from the RRC 203, processes the control message in an RLC #1 261 and an RLC #n 262 by considering characteristics of the control message, and transmits the processed control message to the LC/MAC 208 through a logical channel 207. Further, the L2/RLC 206 receives data from the L2/PDCP 204 and the L2/BMC 205, processes the data in an RLC #1′ 263 and an RLC #n′ 264 and transmits the processed data to the LC/MAC 208 through the logical channel 207. The number of RLCs formed in the L2/RLC 206 may depend on the number of radio links between the UE and the UTRAN.
The logical channel 207 is classified into a dedicated type logical channel for a predetermined UE and a common type logical channel for a plurality of UEs. Further, the logical channel 207 may be classified into a control type logical channel used for transmitting messages including data about control information and a traffic type logical channel used for transmitting messages including data about traffic information.
The type and functions of the logical channels 207 used in the 3GPP are shown in Table 2.
TABLE 2Channel NameFunctionBCCH (broadcastUsed for downward transmission from UTRANcontrol channel)to UE and for transmitting control informationof a UTRAN systemPCCH (pagingUsed for downward transmission from UTRAN control channel)to UE and for transmitting control informationto UE when a position of a cell includingUE is not knownCCCH (commonUsed for PtM control information transmissioncontrol channel)between UE and a network and used when UE hasno connection channel for RRCDCCH (dedicatedUsed for PtP control information transmissioncontrol channel)between UE and a network and used when UE hasa connection channel for RRCCTCH (commonUsed for PtM control information transmission transport channel)between a network and a plurality of UEsDTCH (dedicatedUsed for PtP control information transmission transport channel)between a network and a UE
The L2/MAC 208 manages radio resources and a connection between the UE and the UTRAN under the control of the RRC 203. Therefore, the L2/MAC 208 receives corresponding logical channels as shown in Table 2 from the L2/RLC 206 and transmits the corresponding logical channels to the L1 210 by mapping the corresponding logical channels with transport channels 209 represented in Table 3.
TABLE 3Channel nameFunctionBCH (broadcastMapped with BCCH to transmit data of BCCHchannel)PCH (pagingMapped with PCCH to transmit data of PCCHchannel)RACH (randomUsed for network access and for transmitting controlaccess channel)messages and short data from UE to a networkMapped with DCCH, CCCH, or DTCHFACH (forwardUsed for transmitting control information messages oraccess channel)data from a network to UE or predetermined UEsMapped with BCCH, CTCH, CCCH, DTCH,or DCCHDCH (dedicatedUsed for transmitting data and control informationchannel)messages between a network and UEMapped with DCCH or DTCHDSCH (down-linkDownstream channel used for transmittingshared channel)mass storage data from a network to UEMapped with DTCH or DCCHHS-DSCH (highDownstream channel from a network to UE and havingspeed DSCH)improved transmission efficiency as compared withDSCHMapped with DTCH or DCCH
Although it is not illustrated in Table 3, other transport channels, such as an up-link shared channel and a common packet channel, can be used. However, because the transport channels are not directly associated with the present invention, the detailed description thereof will be omitted.
The transport channels 209 transmitted to the L1 210 illustrated in FIG. 2 are processed through a proper procedure corresponding to real physical channels and transmitted to the UE or the UTRAN. The physical channels include a primary common control physical channel (P-CCPCH), a secondary common control physical channel (S-CCPCH), a paging indicator channel (PICH), an acquisition indicator channel (AICH), a physical common packet channel (PCPCH), etc. Herein, a BCH is transmitted through the P-CCPCH, and a PCH and an FACH are transmitted through the S-CCPCH.
In order to provide the predetermined MBMS, basic information and service guide information on the MBMS must be transmitted from the UTRAN 110 to a plurality of UEs. If the UE 230 having received the basic information and service guide information on the MBMS wishes to receive MBMS, the UE 130 is registered in the CN 100, which is called “joining”. A list of the UEs including the UE 130 and requesting the MBMS is transferred to nodes (e.g., the BM-SC, and the SGSN) included in the CN 100 and the UTRAN.
The CN 100, having received the list of the UEs requesting the predetermined MBMS, and UTRANs 110 and 120, which are connected to the CN 100, transmit a paging message to the UEs including the UE 130. A radio bearer (RB) is set in order to provide the MBMS to the corresponding UEs. Accordingly, the CN 100 can provide the MBMS to the UEs through the set RB.
When the MBMS has ended, it must be transferred to the all UEs. Therefore, the CN 100 and the UTRAN 120 having controlled the UEs release radio resources assigned to the UEs for the MBMS, in order to end the MBMS.
In the state in which the MBMS is provided to the UEs, a plurality of control messages relating to the MBMS are transmitted to the UEs to receive the MBMS. Herein, it is necessary to provide a method effectively capable of informing the UEs of the existence of the control messages.
Currently, the 3GPP has discussed scheme for using a conventional paging method used in voice communication or packet communication as a paging method in the MBMS.
FIG. 3 illustrates a paging procedure for reporting the existence of control information for a conventional MBMS and FIG. 4 illustrates a structure of a conventional paging indication channel.
Referring to FIG. 3, a method for paging a UE for voice communication or packet communication uses a PICH 301 and an S-CCPCH 302. The S-CCPCH 302 contains a PCH (transport channel) through which a PCCH is transmitted. The structure of the PICH 301 is illustrated in FIG. 4. The PICH 301 can transmit 288 bits for a radio frame (basic unit of a physical channel transmission in the 3GPP) with a length of 10 ms, classifies UEs into paging groups, and pages the paging groups. The number of the paging groups may become one of 144, 72, 36, and 18 and the number of bits used in a PI of each paging group may become 2, 4, 8, or 16.
The UE powers on a receiver after predetermined time periods according to a discrete reception (DRX) period determined by a CN and confirms the PICH 301 assigned to the UE. This enables power of the UE receiver to be turned off when the UE does not have to continuously receive a radio signal, thereby preventing the power consumption of the battery of the receiver.
In FIG. 3, the UE paging occasion (PO) 311 is a value calculated by the DRX cycle of the UE. When a paging indicator (PI) of a PICH received in the PO 311 has a positive value, the UE receives the S-CCPCH 302 transmitted after 7680 chip (about 2.00 ms). Further, the UE determines if a PCCH/PCH transmitting a paging message for the UE exists through the S-CCPCH 302. When the paging message for the UE does not exist, the UE turns off the receiver until the next PO. When the PI of the PICH received in the PO 311 has a negative value, the UE turns off the receiver and waits the next PO.
A method for informing the UE of whether a control message regarding an MBMS exists or not and data is transmitted or not uses the PICH 301, an MBMS PO 312, the S-CCPCH 302, or an S-CCPCH 303. The PICH 301 is a channel for informing the UE or other UEs of the existence or absence of a paging for voice call or packet call and the MBMS PO 312 set in all MBMSs or according to each MBMS is dedicated for a paging about the MBMS. An MBMS control channel (MCCH) transmitting control information on the MBMS is transmitted through the S-CCPCH 303. The S-CCPCH 303 may become an S-CCPCH different from the S-CCPCH 302. The S-CCPCH 302 can be used when a message for reporting the existence or absence of the control message regarding the MBMS is transmitted through the PCCH. It is assumed that the MCCH transmits the message for reporting the existence or absence of the control message regarding the MBMS.
Hereinafter, a process for enabling the UE to recognize the existence or absence of the control message regarding the MBMS will be described. More specifically, the UE having turned on the receiver in the MBMS PO 312 receives a PI on an MBMS in which the UE has joined. The length of the MBMS PO 312 may be identical to or smaller than the length of one radio frame (10 ms) constituting a PICH. When the received PI on the MBMS has a positive value, the UE receives the S-CCPCH 303 and receives the message enabling the UE to recognize the existence or absence of the control message on the MBMS.
The conventional paging method for reporting whether the control message on the MBMS exists or not and whether MBMS data is transmitted or not has the following problems.
First, conventionally, PICHs used by UEs that do not support an MBMS are dedicated for an MBMS PO. Therefore, UEs having a PO overlapping with the MBMS PO may unnecessarily demodulate an S-CCPCH. Further, when the MBMS PO is defined according to each service, a UE having joined in a plurality of MBMSs does not have enough time to turn off a receiver. Therefore, a battery of the receiver may be wasted.
Secondly, when UEs having joined in an MBMS have a DRX cycle defined on the MBMS or a DRX cycle defined according to each MBMS in addition to a DRX cycle owned by the UEs, the UEs must frequently turn on the receiver. Consequently, it is difficult to use the DRX cycle.